1. Field of the Invention
The present invention relates to an electromechanical-electroacoustic transducer with low thickness and high travel range, in particular for loudspeakers, as well as to its manufacturing method.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
U.S. Pat. No. 6,359,997 discloses a loudspeaker comprising a magnetic ring composed of multiple radially magnetized magnets disposed with lateral sides in adjacent position. Radial magnetization implies that magnetic flux lines radially converge towards a point that is the center of the transducer, and therefore said magnetic ring is only suitable for circular transducers.
Moreover, the magnetic ring is supported by a mandrel mounted in the transducer basket and therefore said magnetic ring is not a self-supporting element. Said transducer provides for elastic suspensions that connect the mobile coil to the basket. However, the provision of the mandrel to support the magnetic assembly and the presence of suspensions do not permit to obtain an especially thin transducer with respect to the travel range to be obtained.
JP 2006 060333 discloses a loudspeaker comprising a single toroidal magnet subjected to galvanizing metallization surface treatment to prevent early oxidation of magnet. The selection of the surface coating depends on the electrochemical characteristics of the magnetic material. The low thickness of the coating permits to control eddy currents. In fact, in such loudspeaker eddy currents must be reduced because they are especially present in the iron used for the polar expansion that supports the magnet. However, having an extremely low thickness (in terms of microns—0.001 mm), such coating of the magnet is not a self-supporting structure.
Moreover, such a transducer is not able to slow down the motion of the coil by controlling the mechanical attenuation of the mobile assembly, because the thin coating of the magnet does not permit the creation of a significant counter electromotive current. The galvanizing treatment does not exceed a certain thickness and controls only eddy currents in high frequency, being unable to act as short circuit ring useful to control distortion effects at low frequencies, also because of the mechanical attenuation control of the coil motion.
US 2004/213431 discloses a loudspeaker using two vertically magnetized solid rings of magnetic material, with opposite magnetic directions assisted by polar expansions of laminated ferromagnetic material. With such a solution it is impossible to manufacture large transducers, or thin transducers with respect to the linear travel range, or low-weight transducers because of the large quantity of laminated iron used. Moreover, suspension is comparable to a pneumatic one that can be pressurized.
EP 1 553 802 discloses a loudspeaker similar to US 2004/213431, but with three solid magnetic rings characterized by three different magnetic directions. Therefore, the same drawbacks of US 2004/213431 are experienced. Moreover, in these two patent documents, because of the presence of magnets with opposite magnetic directions, magnetic fluxes are generated at the ends of the magnets, with opposite direction and intensity comparable to the central flux, and therefore with braking effects for the main central coil. In fact, in order to use the two fluxes with inverted direction—under and over—other two coils disposed on the same axis as the main coil are used, respectively one in under position and one in over position, with inverted direction with respect to the central coil. Consequently, the coils cannot reach significant travel ranges with respect to the total thickness.
WO 97/09859 discloses a shaker wherein the coil can never reach a significant travel range. Moreover, the coil is never underhung, but always overhung, and the transducer uses two magnetic disks with opposite direction and iron polar expansion.
U.S. Pat. No. 3,979,556 discloses a loudspeaker with a traditional magnetic system, provided with iron polar expansions, disposed towards the periphery of the transducer. Such a solution allows for changing the shape, although with great difficulties. In fact, because of the presence of a gap with large diameter and any shape, two concentric subgaps that are extremely difficult to control are present upon assembly. Such a solution is not easy to make, is heavy because of the large use of iron and does not reach significant travel ranges with respect to the total thickness, regardless of the external diameter.
The purpose of the present invention is to eliminate the drawbacks of the prior art by providing an electroacoustic transducer that permits to manufacture loudspeakers with large diameters, reduced thickness and high travel range of the mobile assembly with respect to total thickness.
Another purpose of the present invention is to provide a transducer wherein magnets are simple to manipulate, not bulky, protected against damage, axially magnetized and adapted to any type of shape and size of the transducer, in spite of starting from the same magnet.
An additional purpose of the present invention is to provide a transducer wherein the coil is as large as possible to dissipate a large amount of heat, thus improving thermal behavior at high powers.
Another purpose of the present invention is to provide a transducer that is simple, reliable, inexpensive and easy to make.
Another purpose of the present invention is to obtain the largest radiant surface possible with the same external diameter.
Another purpose of the present invention is to eliminate any type of magnetic circuit made of iron (polar expansions, plates, T-Yokes, etc.).
Another purpose of the present invention is to provide an electroacoustically powerful transducer that is light and sturdy.
These purposes are achieved according to the invention, with characteristics claimed in the attached independent claims.